How to Make It
In a medium bowl, combine 1 tablespoon of the oil with 1 teaspoon of the hot sauce, the soy sauce and 1/2 teaspoon of the sugar. Add the chicken and toss to coat. Refrigerate for 1 hour or overnight.
Heat a large nonstick skillet over moderately high heat. Add the chicken, season with salt and pepper and cook, shaking the pan occasionally, until browned and just cooked through, 4 to 5 minutes. Transfer the chicken to a plate.
Heat the remaining 1 teaspoon of oil in the skillet. Add the scallions and watercress stems and cook until crisp-tender and lightly browned, 2 to 3 minutes. Add the watercress leaves and cook, stirring, until wilted, 1 to 2 minutes. Transfer the watercress to the plate with the chicken.
Add the coconut milk, lime juice, remaining 2 teaspoons of hot sauce and 1/2 teaspoon of sugar to the skillet. Bring to a simmer and cook until reduced by one-third, about 5 minutes. Stir the chicken and watercress into the sauce, season with salt and pepper and warm through. Add the cilantro and serve immediately.